1. Field of the Invention
The present invention is directed to a system and method for detecting and locating underground objects such as gas, electric, telephone, water utilities, etc. In particular, the present invention provides such a system and method that includes a sensor and positioned RF transmitter receivers that allow determination of the locations of underground objects.
2. Description of the Related Art
Conventional practice for locating underground objects such as underground utilities is a manual, audio technique where a technician uses a hand-held sensor with audio feedback. In the example of underground utilities, the technician first places the sensor at a location where the target utility is assumed to be located. The technician then manually searches for the presence of the underground utility using the sensor based on the audio feedback. Once a portion of the underground utility is found, the technician utilizes the sensor to track the location of the utility, again, based upon the audio feedback of the sensor. The technician then makes paint marks on the ground over the underground utility so that this location can be subsequently mapped and be used by an excavator to identify the expected location of the utility.
In more recent cable locating methods, the operator uses a conventional cable locator to find a cable as described above. However, instead of using paint to mark the location of the cable, a Global Positioning System (hereinafter xe2x80x9cGPSxe2x80x9d) is used to obtain GPS data that marks the location of the cable. In such systems, the technician manually locates a cable sensor over the cable in a manner similar to the conventional practice described above. Then, as the technician manually tracks the cable using the cable locator, he/she periodically marks the location of the cable locator using the GPS system to thereby record the cable location. This technique is disclosed in U.S. Pat. No. 5,576,973 to Haddy.
The technique for locating cables using GPS as disclosed in the Haddy patent has various limitations. In particular, GPS data alone may not be sufficiently accurate in many instances to track a small underground objects and utilities, such as a cable, without additional locating data. At the time of the Haddy patent, the typical accuracy obtainable using a commercially available GPS receiver was between approximately 20-100 meters. This is far too inaccurate to allow effective use in locating an underground cable, especially when the sensor used to locate the underground cable must be moved about in search for the underground cable.
Recently, commercial GPS systems have increased in accuracy. However, their accuracy is still too limited for use with a sensor that is moved about in search of underground objects. In particular, GPS satellites in orbit thousands of miles above the earth broadcast data to a GPS receiver which determines its location in terms of latitude and longitude by calculating the distance to the transmitting satellites. Hence despite improvements to commercial GPS systems, in areas where a clear line of sight to the sky is not available such as in a city with tall buildings, or in more rural areas with tall trees, errors resulting from a GPS based system increases.
Therefore, there still exists a need for a system that can more accurately detect and locate underground objects such as underground utilities, when compared to available GPS based systems.
In addition, there still exists a need for such a system for detecting and locating underground objects in a cost effective manner.
Furthermore, there still exists a need for such a system that is not inhibited by tall buildings or tall trees.
Moreover, there still exists a need for a method for more accurately detecting and locating underground objects.
These and other advantages are attained by a system for detecting and locating an underground object in accordance with one embodiment of the present invention comprising a plurality of stationary transmitter receivers operating in a radio frequency, the plurality of stationary transmitter receivers defining a coordinate system for an area of interest, a sensor adapted to detect of an underground object and to provide presence data upon detection of the underground object, and a mobile transmitter receiver operating in a radio frequency, the mobile transmitter receiver being movable with the sensor and adapted to receive and/or transmit location data indicative of location of the mobile transmitter receiver in the coordinate system.
In accordance with another embodiment, the system also includes a data logger adapted to record the presence data and/or the location data. The data logger may be integral with the mobile transmitter receiver. In accordance with one embodiment, the location data is indicative of distance between the mobile transmitter receiver and at least one of the plurality of stationary transmitter receivers.
In accordance with still another embodiment, the system further comprises a processor unit adapted to store and process the presence data and/or the location data to generate a mapping of the underground object in the coordinate system. In addition, the processor unit also includes a display device for displaying the generated mapping of the underground object. In one implementation, the processor unit is connected to the mobile transmitter receiver and/or one of the plurality of stationary transmitter receivers and is implemented as a hand held computer.
The sensor may be an electromagnetic, a magnetic, or a radio detection sensor, and the underground object may be an underground utility such as gas, electric, telephone, fiber optics, cable, water, and/or sewage utility. The radio frequency may be in a range between 900 MHz to 5.8 GHz. In this regard, in another embodiment, the mobile transmitter receiver and/or the stationary transmitter receivers include a spread spectrum radio circuit having a data processing circuit adapted to determine propagation times of the location data. In one implementation, the data processing circuit is further adapted to determine distance between the mobile transmitter receiver and at least one of the plurality of stationary transmitter receiver based on the propagation times.
In accordance with another aspect of the present invention, a method for detecting and locating an underground object is provided including the steps of establishing a coordinate system for an area of interest, detecting an underground object and providing presence data upon detection of the underground object, and transmitting and/or receiving location data in a radio frequency, the location data being indicative of location of the underground object in the established coordinate system. In one embodiment, the step of establishing a coordinate system includes the step of arranging a plurality of stationary transmitter receivers operating in a radio frequency proximate to the area of interest.
In accordance with one embodiment, the established coordinate system is a relative coordinate system. In this regard, the method may further include the step of fixing the relative coordinate system to a fixed object in the area of interest to establish a fixed coordinate system. Alternatively, the method may include the step of fixing the relative coordinate system by determining global position of at least one of the plurality of stationary transmitter receivers. The underground object may be detected using a sensor which is preferably electromagnetic, magnetic, radio frequency, radiation, metal, and/or chemical detection sensor.
In another embodiment, the method further includes the step of moving a mobile transmitter receiver to location where the underground object is detected. The location data is indicative of distance between the mobile transmitter receiver and at least one of the plurality of stationary transmitter receivers. Alternatively, the method includes the steps of determining propagation times of the location data, and determining distance between at least one of the plurality of stationary transmitter receivers and the mobile transmitter receiver based on the propagation times.
The method may also include the step of processing the presence data and/or the location data to generate and display a mapping of the underground object in the coordinate system. The method may further include the step of recording the presence data and/or the location data.
In still another embodiment, the method further includes the step of moving the plurality of stationary transmitter receivers to an adjacent area that is adjacent to the area of interest, and establishing an adjacent coordinate system for the adjacent area. In this regard, the method of this embodiment also includes the steps of detecting the presence of an adjacent underground object in the adjacent area and providing adjacent presence data upon detection of the adjacent underground object. Moreover, the method further includes the step of at least one of transmitting and receiving adjacent location data in a radio frequency, the adjacent location data being indicative of location of the adjacent underground object in the established adjacent coordinate system.
These and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments of the present invention when viewed in conjunction with the accompanying drawings.